Low birth weight, failure to thrive, hypoplastic anemia and exocrine pancreatic dysfunction are often seen in infancy.  Precursor cells in the marrow show typical vacuolization. Malabsorption and insulin-dependent diabetes often develop.  The pancreas and bone marrow may become fibrotic.  Patients with the classic syndrome as a child can develop features of the Kearns-Sayre syndrome if they survive childhood.  Progressive muscle weakness in pharyngeal, facial, neck, and limb muscles is sometimes seen in older individuals and muscle biopsy reveals ragged-red fibers characteristic of mitochondrial disease.  Some patients have an organic aciduria and others develop hepatic failure with elevated transaminase, bilirubin and lipid levels.  Kidney damage results in Fanconi syndrome.  Young children may recover from the refractory anemia eventually but metabolic acidosis with life-threatening lactic acidosis is a constant threat and responsible for many childhood deaths.